• U.S.

Medicine: Clue from the Cat

4 minute read
TIME

Is cancer contagious? Only a few years ago, most doctors would have answered this question with an emphatic “No!” Now their replies are likely to be less dogmatic. Researchers have long suspected that cancer viruses can be passed genetically from parents to offspring in both animals and humans. A team of veterinarians and cancer researchers headed by Dr. William D. Hardy Jr., 33, of New York’s Memorial Sloan-Kettering Cancer Center, has just reported in Nature that among cats, at least, one animal can infect another with the virus that causes leukemia.

Feline leukemia virus (FeLV) was first identified in 1964 by a Scotsman named William Jarrett; it has since been determined that FeLV can be found in 90% of all cats with leukemia-like illnesses. But this is the first large-scale study showing that it could be spread from one cat to others. That fact is significant both for veterinary and human medicine. Leukemia occurs in cats about 2½ times as often as it does in man. Furthermore, says Hardy, “dogs and cats live with us. They are under the same household stresses and are exposed to the same environmental problems. They often eat the same food. They are also less inbred and thus closer to human genetic patterns than laboratory mice.”

Clustered Cases. The team’s discovery was triggered by the observation that feline leukemia tends to occur in clusters; when one cat in a household comes down with the disease, other unrelated animals develop it too. Intrigued by this pattern of illness, Hardy and his colleagues began testing as many cats as they could for the presence of FeLV, which is carried in platelets, an important blood component, and in white blood cells.

The tests, made at Manhattan’s Animal Medical Center, the A.S.P.C.A., and Boston’s Angell Memorial Hospital, seem to provide convincing evidence that feline leukemia is contagious. Simple blood tests made on 1,462 apparently healthy pet cats from disease-free households showed that only two cats carried FeLV. But of 543 cats from FeLV-infected households, 177 harbored the virus, and many of these later developed leukemic disease. Of the 148 cats from this group that researchers continued to study, 35, or 23.7%, died within six months—24 of them from leukemia, 11 from an FeLV-related anemia. The normal leukemia incidence for the general cat population over the same period is 18.3 cases per 100,000 animals, or .018% for the group studied. Thus the actual incidence of leukemia was about 900 times greater than expected.

Lethal Litter. Hardy has found FeLV in cat blood, saliva and urine; he believes that the animals may spread the virus through their fighting and mating habits, which involve biting, and their grooming practices, which include using their tongues for bathing themselves and their companions. But he also believes that litter boxes are a possible source of the lethal disease. He points out that while many cat owners keep more than one cat, few have more than one box for their animals.

Though infection with FeLV can be fatal for cats, Hardy stresses that humans have little to fear from their pets, even if the animals are found to carry the virus. There is no evidence to date that FeLV can infect humans. But this does not mean that so-called horizontal transmission of cancer is confined to cats. Studies in New York (TIME, June 28, 1971) have shown that Hodgkin’s disease, a cancer of the lymphatic system, occasionally occurs in more-than-coincidental clusters, and suggest that in rare cases the disease may be infectious. An outbreak that affected eight children in Illinois more than a decade ago has stirred similar speculation about leukemia. Hardy’s study can only strengthen the suspicion that human cancer viruses, none of which have been positively identified, could be passed from one person to another.

But there is also a bright side to the work of Hardy’s group; it raises hope that virus-caused cancers in humans may some day be controlled. Team members are already seeking to develop a vaccine against FeLV. Once human cancer viruses are identified, it may be possible to apply similar techniques to battle them.

More Must-Reads from TIME

Contact us at letters@time.com